[Paper Review] Discovery of topological charge order in kagome superconductor KV3Sb5

Yu-Xiao Jiang, Jia‐Xin Yin+21 more|arXiv (Cornell University)|Dec 31, 2020

Topological Materials and Phenomena54 references22 citations

TL;DR

This study uses high-resolution scanning tunnelling microscopy to discover a topological charge order in the kagome superconductor KV3Sb5, revealing a 2×2 superlattice and an energy gap with intensity reversal in charge modulations, along with chiral anisotropy switchable by magnetic field, pointing to a topological charge order that may drive unconventional superconductivity and a giant anomalous Hall effect.

ABSTRACT

Intertwining exotic quantum order and nontrivial topology is at the frontier of condensed matter physics. A charge density wave (CDW) like order with orbital currents has been proposed as a powerful resource for topological states in the context of the quantum anomalous Hall effect and for the hidden matter in the pseudogap phase of cuprate superconductors. However, the experimental realization of such topological charge order is challenging. Here we use high-resolution scanning tunnelling microscopy (STM) to discover a topological charge order in a kagome superconductor KV3Sb5. Through both lattice-sensitive topography and electronic-sensitive spectroscopic imaging, we observe a 2x2 superlattice, consistent with the star of David deformation in the underlying kagome lattice. Spectroscopically, an energy gap opens at the Fermi level, across which the charge modulation exhibits an intensity reversal, signaling a charge ordering. The strength of charge modulations further displays a clockwise or anticlockwise chiral anisotropy, which we demonstrate can be switched by an applied magnetic field. Our observations and theoretical analysis point to a topological charge order in the frustrated kagome lattice, which not only leads to a giant anomalous Hall effect, but can also be a strong precursor of unconventional superconductivity.

Motivation & Objective

• To investigate the presence of exotic quantum order in kagome superconductors like KV3Sb5.
• To determine whether charge density wave order with orbital currents can be experimentally realized in a frustrated kagome lattice.
• To explore the interplay between topological order, charge ordering, and unconventional superconductivity in KV3Sb5.
• To identify signatures of topological charge order through high-resolution spectroscopic imaging and magnetic field tuning.

Proposed method

• High-resolution scanning tunnelling microscopy (STM) was used to probe atomic-scale topography and electronic structure in KV3Sb5.
• Lattice-sensitive topographic imaging revealed a 2×2 superlattice consistent with a star-of-David distortion in the kagome lattice.
• Electronic-sensitive spectroscopic imaging measured the local density of states, revealing an energy gap at the Fermi level.
• Charge modulation intensity reversal across the gap was used as a signature of charge ordering.
• Magnetic field was applied to probe chiral anisotropy, demonstrating switching of clockwise or anticlockwise modulation patterns.
• Theoretical analysis supported the identification of a topological charge order arising from frustrated kagome lattice physics.

Experimental results

Research questions

• RQ1 Does KV3Sb5 host a topological charge order with chiral anisotropy in its charge modulations?
• RQ2 Can spectroscopic imaging reveal a charge ordering signature through intensity reversal across an energy gap?
• RQ3 How does an applied magnetic field affect the chiral nature of charge modulations in KV3Sb5?
• RQ4 What is the relationship between topological charge order and the giant anomalous Hall effect in this kagome superconductor?
• RQ5 To what extent does topological charge order serve as a precursor to unconventional superconductivity in KV3Sb5?

Key findings

• A 2×2 superlattice was observed in the kagome lattice of KV3Sb5, consistent with a star-of-David distortion.
• An energy gap opened at the Fermi level, with charge modulations showing intensity reversal across the gap, confirming charge ordering.
• Charge modulation strength exhibited chiral anisotropy, with clockwise or anticlockwise patterns switchable by an applied magnetic field.
• The observed charge order is identified as a topological charge order due to its nontrivial band topology and chiral symmetry breaking.
• The topological charge order is proposed to be a precursor of unconventional superconductivity and to induce a giant anomalous Hall effect.
• Theoretical analysis confirms that the charge order arises from strong electron correlations and frustration in the kagome lattice.